(1) Field of the Invention
The present invention generally relates to a magnetic recording/playback apparatus, and more particularly to a magnetic recording/playback apparatus which is adapted to eliminate crosstalk during a read-after-write mode operation.
(2) Description of the Related Art
A high-density recording video tape recorder having a read-after-write mode is known. In the video tape recorder of the above type, a digital signal is written to a magnetic tape at a high recording density by using recording heads provided on a rotary cylinder, and the recorded signal is read from the magnetic tape by using playback heads provided on the rotary cylinder. The carrier frequency of the above type is higher than that of a normal-density recording video tape recorder, and the video tape recorder of the above type can perform a read-after-write mode operation. During the read-and-write mode, the signal is played back from the magnetic tape by the playback heads immediately after the signal is recorded in the magnetic tape by the recording heads.
The video tape recorder of the above type includes, for example, four recording heads, four playback heads and four erasing heads, and these heads are arranged on a periphery of the rotary cylinder in a given formation around a central axis of the rotary cylinder. The recording heads are comprised of a pair of first recording heads (L-channel and R-channel) and a pair of second recording heads (L-channel and R-channel). The playback heads are comprised of a pair of first playback heads (L-channel and R-channel) and a pair of second playback heads (L-channel and R-channel). The erasing heads are comprised of a pair of first erasing heads (L-channel and R-channel).
The two heads of each pair are arranged 6.34 degrees apart from each other around the central axis of the rotary cylinder. The first recording heads and the second recording heads are arranged 180 degrees apart from each other on the periphery of the rotary cylinder, and these heads are arranged at confronting positions around the central axis of the rotary cylinder. The first playback heads and the second playback heads are arranged 180 degrees apart from each other on the periphery of the rotary cylinder, and these heads are arranged at confronting positions around the central axis of the rotary cylinder. Further, the first erasing heads and the second erasing heads are arranged 180 degrees apart from each other at confronting positions around the central axis of the rotary cylinder.
In the video tape recorder of the above type, the erasing heads on the rotary cylinder are at positions that correspond to the positions of the relevant recording heads when the rotary cylinder is rotated around the center axis in the forward direction by 322 degrees. The playback heads on the rotary cylinder are at positions that correspond to the positions of the relevant recording heads when the rotary cylinder is rotated around the central axis in the reverse direction by 108 degrees.
At a start of a read-after-write mode operation by the video tape recorder of the above type, one of the erasing heads on the rotary cylinder erases the recorded signal on a track of the magnetic tape. After the rotation of the rotary cylinder 322 degrees around the central axis, one of the recording heads writes a digital signal to the track of the magnetic tape at the location of the erasing performed by the erasing head. Further, after the rotation of the rotary cylinder 108 degrees around the central axis, one of the playback heads reads the recorded signal from the track of the magnetic tape at the location of the writing performed by the recording head. These steps are repetitively performed by the erasing heads, the recording heads and the playback heads of the rotary cylinder every time the rotary cylinder is rotated 180 degrees around the central axis of the rotary cylinder.
FIG. 9 is a time chart for explaining crosstalk during the read-after-write mode operation of the video tape recorder of the above type.
In FIG. 9, (A) indicates the recording operations of the first and second recording heads (L-channel), (B) indicates the recording operations of the first and second recording heads (R-channel), (C) indicates the playback operations of the first and second playback heads (L-channel), and (D) indicates the playback operations of the first and second playback heads (R-channel). For the sake of simplification, in FIG. 9, for example, "REC L1" denotes the L-channel first recording head and "REC R1" denotes the R-channel first recording head.
As described above, the two heads of each pair are arranged 6.34 degrees apart from each other around the central axis of the rotary cylinder. There is a difference between the time of the recording by the L-channel recording heads (for example, "REC L1") and the time of the recording by the R-channel recording heads (for example, "REC R1").
As shown in FIG. 9, one of the recording heads (for example, "REC L1" or "REC R1") writes the signal to the magnetic tape, and after the rotation of the rotary cylinder 108 degrees around the central axis, one of the playback heads (for example, "PB L1" or "PB R1") starts reading the recorded signal from the magnetic tape at the location of the writing. At the start of the playback of the playback head "PB L1" or "PB R1", the recording of the recording head "REC L1" or "REC R1" is not yet terminated. Further, during the playback operation of the playback head "PB L1" or "PB R1", one of the subsequent recording heads (for example, "REC L2" or "REC R2") starts writing the signal to the magnetic tape.
As indicated by the dotted-line arrows in FIG. 9, crosstalk may occur on the playback head because the recording current from the recording heads or the erasing current from the erasing heads tend to leak in or mix with the playback signal output by the playback head. The signal-to-noise (S/N) ratio of the playback signal output by the playback head becomes degraded due to the crosstalk.
In order to reduce the degradation of the S/N ratio, a conventional video tape recorder is adapted to use differential inputs of a head amplifier and parallel signal lines. Further, in order to reduce the degradation of the S/N ratio, a conventional video tape recorder is adapted to incorporate an improved error correction and/or a Viterbi decoding in a signal processing circuit of the video tape recorder.
However, the above-mentioned measures taken by the conventional video tape recorders are effective only in reducing the degradation of the S/N ratio but do not yield a substantial elimination of the crosstalk during the read-after-write mode operation. Further, the differential inputs of the head amplifier and the parallel signal lines or the improved error correction and/or the Viterbi decoding require a large-size complicated circuit for the conventional video tape recorder, which will raise the manufacturing cost significantly.